In bobbin winding machines, it is known, for example from German Patent Publication DE 43 36 312 A1, to drive the take-up bobbin by means of a friction roller, i.e., a so-called winding drum, which simultaneously also places the yarn onto the bobbin. In this apparatus the winding drum of each winding station has its own drive, which is triggered by the winding station computer. Often the winding drum drives are designed as electronically commutatable d.c. motors, since such drives are simple in construction and therefore relatively cost-effective. The commutation of the drive current of such d.c. motors is controlled by means of Hall sensors.
Similar Hall sensors are also employed for detecting the rpm of the winding drum drives. Specifically, a sensor system for recognizing the angular rotation of the winding drum provides information representing or indicative of the rpms of the winding drum, which is converted into predetermined winding drum rpm with the aid of known control methods, for example by using a PID regulating device.
However, with these known regulating systems, the regulation of the rotational speed (rpm) of the winding drum always becomes more difficult when the winding drum rotates at a low speed, which is the case in its start-up phase, for example. Because of their relatively coarse angular resolution below a defined rpm, these known sensor systems are no longer capable at low drum speeds (rpm) of providing sufficiently exact information regarding the angular position of the rotor of the drive motor, so that a smooth jerk-free winding drum rotation often is no longer provided. If, for example, a Hall sensor system with two Hall sensors, offset by 90 degrees, and a magnetic ring with, for example, 32 pairs of magnetic poles is available, an angular resolution, and therefore the detection of the rotating movement of the rotor of the drive motor, is only possible in steps of approximately 2.8 degrees.
As indicated by the curve a in FIG. 1, such a relatively coarse angular resolution is insufficient for the desired regulation of the current commutation of a drive motor in order to assure a uniform start-up as well as reverse running during the search for the yarn end of the dynamic system of the drive and winding drum. It can be seen from the curve a in FIG. 1 that the known regulating systems produce a step-by-step acceleration instead of a linear increase of the angular velocity. Such jerky running of the winding drum is disruptive, in particular during the start-up of the winding drum after a yarn splicing operation, since this leads to uneven yarn tension, which has a negative effect both on the yarn quality and the bobbin structure. Also, disruptions in the winding operation can occur in the course of slow running of the winding drum, for example during the search for the yarn preparatory to a splicing operation, because the non-uniform running of the winding drum leads to loop formation in the yarn running up on the cheese, for example.
Although it would be possible to prevent the non-uniform running of the drive motor, and therefore of the winding drum, at low rotational speeds (rpm) by the employment of a sensor system with an appropriately high angular resolution, the costs associated with such highly resolving systems is relatively large. Therefore these systems are quite expensive, wherein the costs greatly rise with the attainable accuracy of the angular resolution.